Select Committee on Environmental Audit Minutes of Evidence


Annex A

Agricultural Pesticides and Wildlife—the basis for current concerns

1.  INTRODUCTION

  This short summary outlines the key areas of concern relating to the effects of agricultural use of pesticides and wildlife. Concerns relate to areas of pesticide abuse and misuse, and to the direct and indirect effects of approved use. It is clear that whilst there are concerns over current measurable impacts on wildlife, many of our concerns relate more towards the lack of understanding of potential risks to wildlife populations. In part this is because evidence for effects on populations is difficult to collect. In part also this is because, especially in the case of indirect effects on farmland bird populations, pesticide use is only one of several recent changes which is likely to have contributed towards observed declines. The relative contribution of pesticides in such cases may be difficult to ascertain, and the measures to effect a recovery may involve factors in addition to those tackling pesticide use.

2.  CATEGORIES OF PESTICIDE IMPACTS ON WILDLIFE

  There are four different areas of concern relating to the impacts of pesticides on wildlife. These are:

    —  direct effects of approved use on non-target species. This includes both lethal and sublethal effects, including primary and secondary poisoning, both acting within the crop and off target (eg in water courses). It includes also the effect of pesticides alone and in combination with other pollutants;

    —  indirect effects of approved use, for example through reduction in prey availability to non-target species, or deterioration in habitat quality;

    —  pesticide misuse—negligent or incorrect use can lead to inadvertent damage to non-target species; and

    —  pesticide abuse—deliberate use to poison a species in contravention of conditions of use.

3.  DIRECT EFFECTS OF APPROVED USE

  3.1  Trials have shown direct effects of pesticides on within-crop populations of invertebrates and wild plants. Monitoring and wide scale studies have shown long-term and large scale declines in such groups although these have generally been less able to show an effect attributable to pesticides alone. It has been possible to demonstrate recovery in a range of species where pesticide use alone (reduction in herbicide and insecticide use) has been manipulated in conservation headlands.

  3.2  It is known that sublethal effects may increase the susceptibility to other mortality factors (such as predation), interfere with behaviour and reduce reproductive success. The risk of sublethal effects of a range of pesticide groups on fish species as well as on aquatic invertebrates are also of concern. Although population effects have not been demonstrated as a consequence of sublethal exposure to modern agricultural pesticides in the UK, this remains an area of poorly evaluated risk.

  3.3  The risks to wildlife of interactions between pesticides, or between pesticides and other pollutants, is also of concern. Although field evidence is lacking for effects on wildlife populations of synergism between pesticides, such effects have been little studied.

  3.4  Toxicological and experimental studies indicate that there are likely to be risks of adverse ecological effects of pesticides at concentrations found in some surface waters. However there have been few studies to examine whether such effects have occurred in the field as a result of agricultural pesticide use. However the serious consequences for aquatic invertebrates arising from synthetic pyrethroids entering water courses following sheep dipping or industrial wool processing have been well documented in recent years.

  A pesticide tax which steered product choice towards the use of more selective products would have benefits in reducing risks of some of the direct effects summarised above. In some cases pesticide management may be as much an issue as product choice. Measures which reduce drift or leaching into water courses (application technology, buffer zones) would need encouragement.

4.  INDIRECT EFFECTS OF PESTICIDES

  The decline in the population of the grey partridge in the UK since the 1960s is attributed in part to the increasingly widespread use of herbicides in arable crops, and hence in the availability of weeds for the invertebrate prey of gamebird chicks. Greater use of insecticides in cereals is likely to have further affected chick survival by reducing invertebrate prey availability in spring. There is convincing evidence that both weed and arthropod prey densities increase in selectively sprayed field edges (conservation headlands) which in turn improves partridge survival. Overall, evidence is accumulating for the existence of mechanisms of indirect effects operating in several other declining farmland bird species in a similar way to the grey partridge, although other factors are likely to play a role and so manipulation of pesticide use alone may not necessarily be the most effective means of achieving any reversal. At present, designs for a pesticide tax do not include consideration of its potential to contribute towards reducing indirect effects of pesticide use.

5.  PESTICIDE MISUSE

  Misuse can arise from careless use, including spillages or overspraying water courses, as well as deliberate misuse. Certain categories of pesticide are involved more frequently than others in pesticide misuse incidents affecting vertebrates, particularly seed and granular treatments and baits including molluscicides and rodenticides. Although mechanisms, such as a pesticide tax, which may restrict the number of occasions when a pesticide is used can reduce the risk of unforseen events (including some "misuse" events) occurring, it is likely that regulation and enforcement will remain the major mechanism for tackling this problem.

6.  CONCLUSION

  Pesticide tax is unlikely to play a significant role in dealing with pesticide abuse or misuse incidents. In other areas of concern it will have a role provided it is carefully designed, but we should be clear that it is as necessary to tackle the way in which pesticides are used as much as what is used, and alternative policy instruments are likely to be needed here.


 
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